1. Field of the Invention
The present invention concerns a pneumatic tire and, more specifically, relates to a pneumatic tire excellent in wet performance and low fuel cost performance.
2. Description of Related Art
In recent years, a demand for decreasing the fuel cost of cars has been increased and technical development capable of coping with lowering of the rolling resistance of tires and the decrease in the fuel cost has been conducted. On the other hand, it has also been demanded for the improvement of moving characteristic, braking and driving performance, abrasion resistance, etc. of tires or improving the driveability or safety of cars.
As the technique of compatibilizing the tire performances described above, a technique of compounding silica in place of or in combination with existent carbon black as a reinforcing filler for rubber compounds used for treads has been disclosed and known by Japanese Patent Application Kokai No. 10-1565.
In addition to the silica compounding technique, Japanese Patent Application Kokai No. 2001-139729 further discloses a technique of compounding a gelled rubber to a rubber compound for making the wet performance and the low fuel cost performance compatible. As described in Japanese Patent Application Kokai No. 2001-139729, while a gelled rubber with a toluene swelling index (Qi) of 15 or more has a performance as a rubber and the tire performance can be improved relatively easily by selecting a gelled rubber having an appropriate glass transition temperature Tg. However, in a case where gelled rubber entangles to each other, it is difficult to uniformly disperse the gelled rubber which sometimes gives undesired effect on the processability or rubber property of the obtained rubber.
For the improvement of the processability and the rubber property as the problem described above, Japanese Patent Application Kokai No. 2005-146053 proposes a rubber compound for use in a tire tread having 100 parts by weight of a rubber ingredient comprising 5 to 50 parts by weight of a gelled rubber with a toluene swelling index (Qi) of 16 to 70, 5 to 90 parts by weight of a dienic rubber synthesized by living anion polymerization and 0 to 45 parts by weight of other dienic rubber, 5 to 100 parts by weight of silica, and 0 to 100 parts by weight of other filler.
According to the technique described in Japanese Patent Application Kokai No. 2005-146053, while the processability and the wet performance of the tire are considered excellent, it does not discloses the compatibility with the low fuel cost performance and it mentions nothing at all for the effect given on other properties of the tire such as abrasion resistance.